The present invention relates to a thin-walled tube, of a porous non-woven material, a membrane being attached to its inside for membrane filtration and in particular for reversed osmosis.
Such a tube of a non-woven material, for example of paper or polyester fibres with a membrane attached on its inside for reverse osmosis, is known per se. Fibrous tubes with a membrane are placed in supporting tubes after a suitable pre-treatment; these latter tubes are for instance made of a synthetic material with apertures. Thereafter, a liquid to be purified flows under high pressure through the inside of the fibrous tubes with membrane. Owing to this high pressure, liquid passes the membrane and arrives in the non-woven layer from which it is discharged via apertures in the supporting tube. It is, however, impossible for the dissolved agents in the liquid to be purified to pass the membrane, even under the influence of high pressure; these agents are discharged therefore together with the liquid as a more concentrated impure solution.
A disadvantage of such a fibrous tube with a membrane is that it is generally very difficult to remove the tube and membrane from the supporting tube when the membrane is worn out. According to the high inner pressure, the non-woven material of the tube is usually pressed against the inside of the supporting tube.
A consequence of the above is that in practice one is generally forced to use vigorous means for removing the non-woven material, which generally results in the apparatus being inoperative for a longer time than is justified in view of its extensive investment cost.
It has been attempted to facilitate the removal of the fibrous tube from the supporting tube by mechanical means, which operation has not heretofore proved satisfactory.